1. Field of the Invention
The present invention relates to a system, method, and program for error handling in a dual adaptor system.
2. Description of the Related Art
In a storage loop architecture, such as the Serial Storage Architecture (SSA), a plurality of disks are interconnected to one or more adaptors so that either of the adaptors can access the one or more loops of interconnected disks. An adaptor may include two or more ports to allow connection to one or more loops. For each loop on which the adaptor communicates, one adaptor port connects to a first disk in the loop and the other port connects to another disk in the loop. Additional adaptors may be added to the loop, such that one port on each other adaptor connects to one disk and another port connects to another disk so that the additional adaptors are placed within the loop. Additional details of the SSA architecture and different possible loop topologies are described in the International Business Machines Corporation (IBM) publication “Understanding SSA Subsystems in Your Environment”, IBM document no. SG24-5750-00 (April, 2000), which publication is incorporated herein by reference in its entirety.
One or more computer systems, such as storage subsystems, host system, etc., may include the adaptors connecting to the loop. Adaptors that share a loop must intercommunicate to coordinate accesses to disks in the shared loop. High end storage systems, such as the IBM Enterprise Storage Server (ESS), can detect errors in the ability of an adaptor in another system to communicate with the local operating system even though such detected adaptor is still capable of communicating on the network. In such instances, the system detecting the problem will delay I/O processing for a timeout period that corresponds to the time required for the other system including the adaptor to initiate an error recovery procedure. This timeout period must take into account all different timeout periods and error recovery procedures that could occur within the detected system unable to communicate with the adaptor. In many cases the timeout period can extend for several minutes.
In storage systems requiring high availability, such as storage systems for critical uses, any delays in I/O processing are generally unacceptable. Thus, extensive delays in I/O processing, such as a delay resulting from the lengthy timeout period for the error recovery process at the detected system, would be unacceptable in a high availability system.
In addition to delays that may result from having to wait for the system housing the other adaptor to reset, additional delays may be incurred when a master adaptor is subject to the reset. The master adaptor, which is the configurator with the highest unique identifier (ID), is responsible for configuring each port in the network with various parameters and coordinating the processing of asynchronous events such as dynamic changes in the network configuration. If a master adaptor is reset, then in the SSA architecture, the adaptor having the next highest unique identifier will be designated as the master. Following reassignment of the master node, each remaining adapter on the loop adjusts internal routing algorithms under direction from the new master initiator, so that frames are automatically rerouted to avoid the break. This allows devices to be removed or added to the loop while the subsystem continues to operate without interruption.
Upon resetting an adaptor, the system will experience a brief I/O delay to coordinate the reset adaptor entering a disabled state. If a slave is reset, then the I/O delay may only be a few seconds. However, if the master is reset, then the I/O delay may double to 8 to 16 seconds due to the additional time needed to switch the master to another adaptor.
For these reasons there is a need in the art to provide improved error handling that reduces timeout delays in systems where two adaptors are capable of accessing the storage devices and reduces delays associated with resetting the master adaptor.